C10orf54 is a single-pass type I transmembrane protein that is 311 amino acids in length and includes a signal sequence and one IgV-like domain in its intracellular region. It is potentially a member of the B7 family of proteins and it has approximately 24% sequence identity to B7-H1/PD-L1 (Flajnik et al., Immunogenetic 64:571-590 (2012)). The mouse ortholog to C10orf54 is known as V-region Immunoglobulin-containing Suppressor of T Cell Activation (VISTA; also known as PD-L3). VISTA was cloned from a library of CD4 positive regulatory T cells (Treg) (Wang et al., JEM 208(3):577-592 (2011)). VISTA is primarily expressed on hematopoietic cells, and VISTA expression is highly regulated on myeloid antigen-presenting cells (APCs) and T cells (Wang et al., supra).
VISTA appears to have functional activities that are nonredundant with other Ig superfamily members and may play a role in the development of autoimmunity and immune surveillance in cancer. For example, expression of a VISTA-Ig fusion protein has been shown to inhibit T cell proliferation and cytokine production in vitro and overexpression of VISTA on MCA105 tumor cells interferes with a host's protective antitumor immunity (Wang et al., supra). Moreover, administration of a VISTA-specific monoclonal antibody enhanced CD4 positive T cell response in vivo and the development of autoimmunity (Wang et al., supra). Monoclonal antibodies against C10orf54 have also been shown to prevent acute graft-versus-host disease in mice (Flies et al., J. Immunology 187(4):1537-1541 (2011)). Citation or discussion of a reference herein shall not be construed as an admission that such is prior art to the present disclosure.